a device used in spectroscopy to measure wavelengths by interference effects produced by multiple reflections between parallel half-silvered glass or quartz plates
Word origin
C20: French étalon a fixed standard of weights and measures, from Old French estalon; see also stallion
etalon in American English
(ˈeɪtəˌlɑn)
noun
an optical instrument with two plane parallel reflecting surfaces, used for the precise measurement of distance or the wavelength of light